Concerns had been raised that approvals could lead to a flood of deals that put control of Canada’s vast energy resources in Chinese hands, but Harper said the approvals should be seen as the end of a trend and not the beginning.

He said no other industrialized country would allow a major sector of its economy to be taken over by state-owned companies from another country.

The prime minister noted that 15 companies dominate production in the Alberta oil sands and said the sector represents 60 percent of all the oil production around the world that is not already in state hands.

He feared a few larger purchases by foreign state-owned companies could rapidly transform the industry from one that is essentially a free market industry to one that is effectively under the control of a foreign government.

Canada’s new position may not go over well in China where they are eager for an even greater share of Canada’s oil. Alberta has the world’s third-largest oil reserves after Saudi Arabia and Venezuela: More than 170 billion barrels.

Daily production of 1.5 million barrels from the oil sands is expected to increase to 3.7 million in 2025.

CNOOC and other big state-owned Asian energy companies have increased purchases of oil and gas assets in the Americas as part of a global strategy to gain access to resources needed to fuel their economies. Chinese companies have moved more carefully since CNOOC tried seven years ago to buy Unocal, but was rejected by US lawmakers, who cited national security fears.

Harper’s government originally turned down Petronas’ bid for Progress Energy in October.

The government did not publicly explain the decision to block the deal, but said a new policy framework for foreign takeovers would be released soon. Petronas was allowed to re-apply.

The decision to turn it down in October raised doubts about whether Canada is open to foreign investment.

The government also rejected Anglo-Australian BHP Billiton’s hostile takeover bid for Potash Corp in 2010 and the sale of Vancouver-based MacDonald, Dettwiler and Associates’ space-technology division to a US company in 2008.

However, Harper has lobbied the Chinese to invest in Canada’s energy sector and has said billions in foreign investment is needed to develop Canada’s vast oil and gas deposits.

Harper said the Nexen transaction by itself did not raise fears.

Most analysts believed the deal would be approved because more than 70 percent of Nexen’s assets are outside Canada. Analysts say a company like Suncor, Canada’s largest oil company, would have been off limits.